This invention relates generally to a subsystem and method for detecting and plotting the perimeter of an object being inspected with a system using a charge coupled device (CCD) as the detection element and particularly to such a subsystem and method for detecting and plotting the perimeters of the phosphor screens on kinescope panels.
U.S. application Ser. No. 388,143 entitled "CHARGE COUPLED DEVICE BASED INSPECTION SYSTEM AND METHOD" filed June 14, 1982 by Robert A. Duschl, now U.S. Pat. No. 4,454,545, discloses an inspection system employing a CCD. The system is very versatile and permits replacing the CCD with a CCD having different characteristics, such as different numbers of rows and columns of pixels or which is responsive to a different type of energy. When a CCD is replaced, the numbers of rows and columns of pixels of the replacement CCD are set into the system and the waveform generator is reset in accordance with the transfer characteristics of the replacement CCD. The system is then ready for use with the replacement CCD.
U.S. application Ser. No. 388,038 entitled "CHARGE COUPLED DEVICE BASED BLEMISH DETECTION SYSTEM AND METHOD" filed June 14, 1982 by Robert A. Duschl, now U.S. Pat. No. 4,454,541, discloses a system and method for detecting blemishes on the screen of a kinescope. Blemishes are detected by comparing the signal on each CCD pixel with the average of the signals on the immediately adjacent pixels and generating a blemish signal when the difference exceeds a predetermined threshold.
U.S. application Ser. No. 388,029 entitled "CHARGE COUPLED DEVICE BASED SYSTEM AND METHOD FOR MEASURING PROJECTED FIGURES" filed June 14, 1982 by Robert A. Duschl, now U.S. Pat. No. 4,480,264, describes a system for measuring figures projected onto a CCD. The data from a number of adjacent pixels in a particular line is summed, and the summed signal is divided by a maximum signal to provide a mean pixel signal which is multiplied by a dimension per pixel value to provide a dimensional signal representative of the dimension being measured.
U.S. application Ser. No. 388,037 entitled "CHARGE COUPLED DEVICE BASED SYSTEM AND METHOD FOR INSPECTING AND MODIFYING IMAGES" filed June 14, 1982 by Robert A. Duschl describes a system employing a CCD for inspecting or modifying images. An image of the device being inspected is cast onto a CCD and compared with a reference image to identify and locate faults in the object. The disclosures of these applications are incorporated by reference herein.
The systems described in the above-referenced applications operate quite satisfactorily for the purposes intended. However, optimization of efficiency when using the systems results in the need for the ability to accurately identify the perimeters of the objects being investigated irrespective of the dimensions and orientation of the objects. For example, in utilizing the blemish detection system described in U.S. application Ser. No. 388,038, the faceplate of a kinescope is accurately positioned and oriented in an inspection system employing a CCD and a camera. Light is passed through the screen of the faceplate panel to charge the CCD pixels to various levels. The pixel charge levels are processed to determine the presence of a blemish within the screen. Prior to processing the individual pixel charge levels, the perimeter of the kinescope screen is synthesized by generating an "electronic mask" around the perimeter of the phosphor screen being inspected. This perimeter generation results in several disadvantages. First, the panel must be accurately oriented in the inspection system and the size of the panel being inspected must be known. Additionally, because of the generation of the electronic mask the pixels in the proximity of the edge of the screen being inspected cannot be considered because they are masked out by the electronic mask.
The instant invention overcomes the above-noted deficiencies by the provision of a subsystem and method for detecting and plotting the perimeter of an object irrespective of the orientation and size of the object.